Torque limiter

ABSTRACT

IN A FLOOR GRINDER, A MOTOR DRIVES A HOLLOW VERTICAL SHAFT. A LOWER SHAFT TELESCOPES INTO THE HOLLOW SHAFT, IS SPRING LOADED DOWNWARD, AND HAS A GRINDING PLATE FIXED TO ITS LOWER PROJECTING END. THE HOLLOW SHAFT HAS AT LEAST ONE SPIRAL DRUM CAM CUTOUT FORMED IN IT AND THE LOWER SHAFT HAS A CAM FOLLOWER EXTENDING INTO THE DRUM CAM CUTOUT SO THAT EXCESSIVE TORQUE IMPOSED BY FRICTIONAL RESISTANCE ENCOUNTERED BY THE GRINDING PLATE CAUSES THE DRUM CAM CUTOUT TO RAISE THE CAM FOLLOWER AND THE LOWER SHAFT AND LIFT THE GRINDING PLATE THEREBY LIMITING TORQUE.

United States Patent 3,552,070 TORQUE LIMITER Peter F. Reiss, Bayside, N.Y., assignor to Oztec Industries, Inc., a corporation of New York Filed Dec. 16, 1968, Ser. No. 783,938 Int. Cl. B24b 23/00, 25/00 US. Cl. 51-177 11 Claims ABSTRACT OF THE DISCLOSURE In a floor grinder, a motor drives a hollow vertical shaft. A lower shaft telescopes into the hollow shaft, is spring loaded downward, and has a grinding plate fixed to its lower projecting end. The hollow shaft has at least one spiral drum cam cutout formed in it and the lower shaft has a cam follower extending into the drum cam cutout so that excessive torque imposed by frictional resistance encountered by the grinding plate causes the drum cam cutout to raise the cam follower and the lower shaft and lift the grinding plate thereby limiting torque.

BACKGROUND OF THE INVENTION This invention relates to floor or terrazzo grinders and the like. Such grinders have one or more vertical motors each of which rotates a grinding plate held against the floor. Soft spots in the floor or other factors causing excessive torque, overload the motors of conventional floor grinders to cause high power demands, blow fuses, burn out the motors, and do other damage.

SUMMARY OF THE INVENTION A floor grinder has at least one motor driving a hollow, vertical shaft. A lower shaft telescopes into the hollow shaft and has a floor grinding plate fixed to its lower projecting end by means of a universal joint. The hollow shaft has at least one spiral drum cam cutout formed in it. A cam follower extends radially from the lower shaft to engage the drum cam. A spring loaded ring bears on an extension of the follower to urge the inner shaft downward and thereby the grinding plate against the floor. Excessive torque imposed by frictional resistance encountered by the grinding plate causes the drum cam to urge the cam follower, the lower shaft, and the grinding plate upward to thus limit the torque.

The construction of the torque limiter of this invention allows a floor grinder with a five horsepower motor to operate at maximum efiiciency with a current fluctuation of less than two amperes. This prevents motor overheating and failure, blown fuses, inefficient operation, and many other problems which beset conventional floor grinders.

The torque limiter of this invention is comparatively inexpensive to fabricate, is automatic and foolproof in its operation, and performs in a superior manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a floor grinder according to this invention;

FIG. 2 is a side view of a hollow shaft with two barrel cam cutouts formed therein; and

FIG. 3 is a longitudinal section through a fragment of a motor and a torque limiting drive according to this invention, the drive having a universal joint fixed to its lower end, the universal joint supporting a grinding plate which is shown partly broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, a floor grinder has a body 11 which rolls on the front and rear wheels 12 and 13. The

Patented Jan. 5, 1971 lCC rear wheel or wheels 13 may be castered to enable the body 11 to be steered. An extension 14 of body 11 supports the handle 15 with which the operator moves the floor grinder 10.

A pair of motors 16 and 17 are mounted on a frame 18 which is pivotally fixed to body 11 at 19. A yoke 20 is fixed to frame 18. Hand wheel 21 turns a threaded shaft (not shown) to draw link 22 rearward or allow it to move forward to raise or lower motors 16 and 17 as frame 18 pivots about 19. Link 22 may include a threaded length adjusting portion 24 so that the length of link 22 may be set to place frame 18 in a desired position when wheel 21 is turned as far as it will go in one direction.

It is to be noted that the two motors 16 and 17 are staggered, one slightly in front of the other, so that their grinding plates grind overlapping areas as the floor grinder 10 is moved forward or backward. Flexible skirts 25 extend below frame 18 to surround the grinding plates.

Referring now to FIGS. 2 and 3, motor 17 is mounted on a portion 26 of frame 18. A tubular support 27 is welded at 28, or otherwise secured, to extend downward from portion 26 about the shaft 29 of motor 17.

A cover 30, to the bottom of which skirts 25 are attached as shown in FIG. 1, surrounds tubular support 27.

By means of key 31, a hollow shaft 32 is fixed to motor shaft 29. Hollow shaft 32 is formed in two parts 33 and 34 which are welded or otherwise joined to allow for the insertion of upper bearing 35. A lower bearing 36 is pressed into the lower end of hollow shaft 32.

A lower annular flange 37 and a retaining ring 38 secure a ball bearing 39 or the like about the lower end of hollow shaft 32. The outer race of bearing 39 fits within a larger diameter portion 40 at the bottom of tubular support 27. A retaining ring 41 may secure bearing 39 therein. The groove 43 within which retaining ring 38 fits may be seen in FIG. 2. A lower shaft 42 is slidably disposed to telescope within hollow shaft 32 while being slidably supported by the bearings 35 and 36.

As may be most clearly seen in FIG. 2, two spiral drum cam cutouts 44 and 45 are formed in hollow shaft 32 to extend upward at an angle of 60 degrees with the horizontal. Referring again to FIG. 3, two cam follower shafts 46 and 47 are screwed or otherwise fixed into lower shaft 42 to project through the drum cam cutouts 44 and 45. Inner cam rollers 48 and 49 on shafts 46 and 47 ride on the drum cam cutouts 44 and 45.

An upper spring retaining ring 50 is welded or otherwise fixed about hollow shaft 32. A lower spring retaining ring 51 is slidably disposed about hollow shaft 32. Compression spring 52 extending between rings 50 and 51 urges ring 51 downward. Outer cam follower rollers 54 and 55 mounted on shafts 46 and 47 receive the downward thrust of spring 52 on ring 51 to urge the telescoping lower shaft 42 downward.

A disk 58 is fixed at the bottom of lower shaft 42 to have a universal joint 59 mounted thereunder. Supported by universal joint 59 is a grinding disk 60. Suitable grease seals (not shown) may be disposed between the lower ends of hollow shaft 32 and tubular support 27 below bearing 35. If desired, a water conducting tube 62 may extend through a hollow motor shaft 29 and the torque limiting device of this invention to the grinding plate 60.

In operation, motors 16 and 17 are lowered by hand wheel 21 to enable springs 52 to force a pair of grinding plates 60 against a floor with a force to enable the motors 16 and 17 to drive the grinding plates 60 with a desired operational torque. If some operational factors, such as a soft spot in the floor or an unevenness, increase the torque, hollow shaft 32 will tend to rotate relative to lower shaft 42 so that the rollers 48 and 49 ride upward in the drum cam cutouts 44 and 45. This raises grinding plate 60 3 to relieve the torque on its motor. Thus it may be seen that the torque limiter of this invention is self-regulating.

If the spring 52 is a spring which exerts a greater force as it is compressed, frame 18 may be lowered to produce any desired operational torque Within the limitation of the compression of spring 52 by the telescoping of the lower shaft 42.

While this invention has been shown and described in the best form known, it will nevertheless be understood that this is purely exemplary and that modifications may be made without departing from the spirit and scope of the invention.

I claim:

1. A torque limiter for use in a floor working machine ha ving a motor and a floor engaging grinding plate driven by said motor, said torque limiter comprising, in combination, a drive shaft formed of two telescoping sections, interengaging means secured to said sections to telescope said sections during relative rotation therebetween, said drive shaft being connected at one free end to said motor and at the other free end to said grinding plate, and resilient means urging said grinding plate from said motor, said engaging means on said shaft sections drawing said plate toward said motor against the urge of said resilient means as the result of relative rotation produced by torque resistance to the rotation of said grinding plate by said motor and said drive shaft whereby said resistance is limited.

2. A device as set forth in claim 1 wherein said resilient means is adjusted to said torque resistance may be limited a predetermined amount.

3. A torque limiter for use in a floor Working machine having a motor and a grinding plate or the like driven by said motor, said torque limiter comprising, in combination, a first shaft, a hollow shaft within which said first shaft rotatably telescopes, one said shafts containing least one drum cam cutout formed at an angle with the horizontal; a cam follower fixed to the other of said shafts extending into and engaging said at least one drum cam cutout, one of said shafts driving the other by means of said cam follower and said drum cam cutout, and resilient means urging said first shaft outward from said hollow shaft, said shafts being vertically disposed, one of said shafts being driven by said motor and the other of said shafts having said grinding plate fixed to its free end so that excessive torque causes said cam follower to move in said drum cam cutout telescoping said shafts against said resilient means to raise said grinding plate to thereby reduce the excessive torque.

4. The combination according to claim 3 wherein said hollow shaft contains said at least one drum cam cutout and said cam follower extending into and engaging said at least one drum cam cutout projects outward from said first shaft.

5. The combination according to claim 4 wherein said hollow shaft is driven by said motor, said first shaft is a lower shaft and has said grinding plate fixed thereto, and excessive torque causes said at least one cam follower to ride upward in said drum cam cutout raising said lower shaft and said grinding plate.

6. The combination according to claim 5 wherein said hollow shaft contains two oppositely disposed drum cam cutouts and where in said lower shaft has two cam followers engaging said drum cam cutouts.

7. The combination according to claim 6' wherein said spring means urging said lower shaft outward from said hollow shaft comprises spring mounting means fixed to said hollow shaft above said drum cam cutouts, a spring retaining ring slidably disposed about said hollow shaft below said spring mounting means, said cam followers having cam follower shafts extending through said drum cam cutouts outward from said hollow shaft, and a compression spring disposed about said hollow shaft and between said spring retaining means and said spring retaining ring, said compression spring urging said retaining ring downward to bear on said cam follower shafts to urge said lower shaft downward.

8. The combination according to claim 7 wherein said cam follower shafts have inner and outer rollers mounted thereon to engage said drum cam cutouts and said spring retaining ring.

9. The combination according to claim 8 wherein said lower shaft has a universal joint to fix said grinding plate thereto.

10. The combination according to claim 9 wherein said compression spring exerts greater force as it is compressed and with the addition of means to adjust the height of said motor to regulate the operational limits of the torque required of said motor to drive said grinding plate.

11. The combination according to claim 10 wherein said drum cam cutouts are formed at 60 degrees with the horizontal.

References Cited UNITED STATES PATENTS 1,571,571 2/1926 Cavicchi 51177 1,392,543 10/1921 Watrous 51177 FOREIGN PATENTS 479,007 3/1953 Italy. 293,432 7/1914 Germany.

JAMES L. JONES, JR., Primary Examiner U.S. Cl. X.R. 

